A copper plating process is widely used in a technique of manufacturing interconnects of semiconductor devices. With the progress toward high integration of semiconductor devices, circuit interconnects become finer and as a result microfabrication in two-dimensional direction is approaching a limit. Thus, a TSV (through-silicon via) technique is expected to be a technique that can further improve a device performance. This TSV technique is a three-dimensional layering technique for fabricating a through-electrode by filling a via-hole with a conductive material, such as copper, to establish an electrical connection between semiconductor chips through the through-electrode.
An important point for filling the metal into the via-hole with no void is to accelerate metal deposition on a bottom of the via-hole while suppressing metal deposition on a field surface of the substrate. Therefore, an accelerator for accelerating the metal deposition and a suppressive-component containing agent (e.g., a suppressor (for example, PEG or polyethylene glycol) and a leveler) for suppressing the metal deposition are typically added to a plating solution. Specifically, in order to fill the via-hole, having a depth of 50 μm to 200 μm, with copper, the suppressive-component containing agent having a very strong suppressive effect must be used. The accelerator and the suppressive-component containing agent may be collectively referred to as additive.
In order to fill the via-hole with metal with no void therein, it is important to control a concentration of an additive during plating. A CVS (Cyclic Voltammetric Stripping) technique is conventionally used for concentration analysis of the additive. However, the additive in the plating solution may produce by-products with the progress of plating, and the by-products may have an adverse influence on the concentration analysis results. As a consequence, the concentration of the additive may not be controlled correctly, and a void may be formed in the metal. Further, characteristics of a plated film, such as a crystal grain size and an orientation of a plated copper, may change due to action of the additive. Therefore, if the concentration of the additive is not controlled properly, the characteristics of the plated film may be varied from substrate to substrate. In particular, in the case of using the suppressive-component containing agent having a very strong suppressive effect, it is difficult to correctly measure the concentration of the suppressive-component containing agent with use of the CVS technique because the by-products affect the analysis.
In order to rapidly fill the via-hole with metal, it has been a conventional practice to increase a current density on a substrate during plating of the substrate. In order to fill the via-hole with metal rapidly while preventing formation of void, it is necessary to increase the current density when the majority of the via-hole is filled with the metal.
However, it is difficult to accurately determine a filling percentage of the metal in the via-hole because the progress of plating is judged based on a plating time. As a result, the current density may not be increased at a proper timing If a timing of increasing the current density is too early, a void is formed in the via-hole. On the other hand, if the timing of increasing the current density is too late, a time required for the plating cannot be shortened.
Typically, a plating end point is controlled based only on the plating time. However, since a manner of the progress of plating is varied depending on a plating process, controlling the plating end point based only on the plating time may result in insufficient plating or excessive plating.